Effects of aspect ratio and component ratio on binary-mixed discharging pebble flow in hoppers

Abstract

As an important class of particle flows in industrial applications, hopper flows, particularly those using pebbles (diameters dp ~O(10-2) m), play a significant role in nuclear reactor engineering, e.g. HTGR and ADS reactors. However, the features and influencing factors of the binary mixture discharge have not yet been widely investigated. In this study, the discrete element method (DEM) simulation was adopted to analyze the discharge flow of binary mixtures consisting of ellipsoids and spheres in a hopper. After a model validation, the effects of particle aspect ratio (Ra, the ratio of the major axis to the minor axis) of ellipsoids and component ratio (Rn, the ratio of the ellipsoid number to the sphere number) of ellipsoids to spheres were analyzed. Flow patterns were visualized by colored pebble stripes according to pebbles' initial heights. Particle discharge flow rates were computed to examine their relations to particle aspect ratios and component ratios. The force structure and distributions of the binary mixtures were also explored. Results showed that pebble stripes followed quadratic function profiles. Adding ellipsoids was advantageous for particles discharging at lower particle aspect ratios (Ra≤2), while impedimental at large particle aspect ratios (Ra≥3). The discharge flow rate was inversely proportional to the particle aspect ratio at fixed component ratios, and linearly proportional to the 1/4th power of the component ratio at fixed particle aspect ratios. In addition, the discharge flow rate showed low sensitivity to the initial packing states of particles when the particle aspect ratio and component ratio were fixed.